Can the crawler reach it
robots.txt, response codes, redirect chains and loops, crawl budget limits, orphaned pages with no internal link at all.
Technical SEO audit
The layer everything else stands on. If a crawler cannot reach or understand a page, content and links do not matter.
Can it understand
JavaScript rendering, differences between server HTML and the rendered DOM, structured data and agreement with visible content.
Will it pick the right address
Canonicals, URL parameters, trailing-slash variants, www and non-www versions, duplication across languages.